Doxy PEP & STI Rates: Is San Francisco Seeing a Drop?

San Francisco has seen a significant decline in cases of syphilis, chlamydia, and gonorrhea, with officials attributing the drop to expanded prevention efforts and increased use of doxycycline post-exposure prophylaxis (doxy-PEP). Between 2024 and 2025, cases of chlamydia fell by 18%, syphilis by 24%, and gonorrhea by 5%, according to the San Francisco Department of Public Health.

The most pronounced decreases were observed among men who have sex with men (MSM) and transgender women, groups historically disproportionately affected by these infections. “The remarkable drop in STI cases in San Francisco is due in large part to the trailblazing work that made the rollout of doxy-PEP possible,” said Dr. Stephanie Cohen, director of STI and HIV prevention and control for the San Francisco Health Department, in a statement.

What is Doxy-PEP?

Doxy-PEP involves taking the antibiotic doxycycline after potential exposure to a bacterial STI – specifically after condomless oral or anal sex – to prevent infection. We see intended for use by MSM and transgender women who have sex with men. Research indicates that doxy-PEP can reduce the risk of chlamydia by 88%, syphilis by 87%, and gonorrhea by 55% in this population.

San Francisco was the first city in the United States to issue guidance on doxy-PEP in 2022. Dr. Susan Phil, San Francisco Health Officer, added that We are excited to see the progress being made in lowering STI diagnoses in San Francisco. We encourage the public to keep up the momentum by taking actions – such as getting tested – to protect their sexual health.

CDC Recommendations

The Centers for Disease Control and Prevention (CDC) recommends that healthcare providers discuss doxy-PEP with MSM and transgender women who have sex with men. The CDC guidelines suggest that individuals in these communities who have had an STI in the past year are particularly good candidates for the preventative treatment.

Concerns About Antibiotic Resistance

The widespread use of doxy-PEP has raised concerns about the potential for increased antibiotic resistance in the bacteria that cause these STIs. Gonorrhea, in particular, has already demonstrated resistance to multiple classes of antibiotics. Some experts fear that increased doxycycline use could accelerate the development of resistance.

An early study indicated that certain types of antibiotic-resistant gonorrhea were becoming more common, leading to questions about whether increased doxy-PEP use might be contributing to this trend. However, more research is needed to determine the extent of this connection. Despite these concerns, experts continue to recommend doxy-PEP, citing data like that from San Francisco which suggests a positive impact on the STI epidemic.

doxy-PEP does not protect against viral STIs such as HIV, HPV, or herpes.

Looking Ahead

The success of doxy-PEP in San Francisco offers a promising approach to STI prevention, but ongoing monitoring of antibiotic resistance patterns will be crucial. Further research is needed to fully understand the long-term effects of widespread doxy-PEP use and to optimize its implementation for maximum benefit.